1. Technical Field of the Invention
The present invention relates in general to wireless communication systems, and in particular, to paging mobile terminals within wireless communication systems.
2. Description of Related Art
Today's wireless telecommunications networks provide telephone subscribers with the ability to access telecommunications services from almost anywhere in the world. The key to facilitating such world-wide access is mobility management. With mobility management, wireless networks are able to track the location of mobile subscribers so that mobile services can be delivered to them.
A wireless network is typically formed of a number of cells, each covering a small geographic area within which a mobile device, such as a mobile station, may receive mobile services. Each cell is equipped with a base station that provides radio coverage to the cell, thereby enabling communication with mobile devices located within the cell. By integrating the coverage of multiple base stations, a wireless network is able to provide radio coverage to mobile subscribers over a large geographic area.
A traditional wireless network 10a is illustrated in FIG. 1. The coverage area of a collection of neighboring base stations is commonly referred to as a location area (LA) 70. Each LA 70 (i.e., LA1-LA5) is served by a Radio Access Node (RAN) 50 (i.e., RAN1-RAN5) and a mobile switching center/visitor location register (MSC/VLR) 30 (i.e., MSC/VLR1 and MSC/VLR2) via a respective connectivity network 40a and 40b. In addition, each MSC/VLR 30 may serve multiple LAs 70, which together form an MSC coverage area 60. For example, LA1-LA3 form MSC1 coverage area that is served by MSC/VLR1, while LA4 and LA5 form MSC2 coverage area that is served by MSC/VLR2.
The MSC/VLR 30 is the network node that provides circuit-switched calling, mobility management and other telecommunications/mobile services to mobile subscribers. In particular, the MSC/VLR 30 maintains subscriber data for all mobile subscribers that are currently located within one of the location areas 70 served by the MSC/VLR 30. For example, the subscriber data for each mobile subscriber typically includes the location area and serving base station of the mobile subscriber, which allows the MSC/VLR 30 to page, communicate with and connect incoming calls to that mobile subscriber.
When a mobile subscriber moves or “roams” into a new location area 70 (e.g., from LA1 to LA2), the mobile device must inform the wireless network of the change in location area by performing what is commonly referred to as a location update procedure. Each mobile device is responsible for maintaining the location area code (LAC) of the current location area and comparing the stored LAC with subsequent LAC's that are broadcast and received by the mobile device. If the mobile device finds that the received LAC is different from the stored LAC, the mobile device sends a location update request to the wireless network.
If the new location area is served by a different MSC/VLR than the previous location area, an inter-VLR location update is performed. For example, if the mobile device roams from LA3, which is served by MSC/VLR1 into LA4, which is served by MSC/VLR2, an inter-VLR location update is performed. During the inter-VLR location update, the new MSC/VLR that receives the location update request from the mobile subscriber transmits an update location message to the Home Location Register (HLR) 20 of the mobile subscriber. The HLR 20 is a database that maintains permanent subscriber records for mobile subscribers. Upon receiving the update location message, the HLR 20 forwards the subscriber data associated with the mobile subscriber to the new MSC/VLR (i.e., MSC/VLR2) for temporary storage in the new MSC/VLR while the mobile subscriber is within the MSC/VLR coverage area and updates its records to indicate that the mobile subscriber is now present in a location area served by the new MSC/VLR. In addition, the HLR 20 asks the old MSC/VLR (i.e., MSC/VLR1) to delete its subscriber record for this mobile subscriber since the mobile subscriber is no longer located in a location area served by the old MSC/VLR.
Once the location update procedure is complete, the mobile subscriber can continue to receive mobile services through the new MSC/VLR (i.e., MSC/VLR2). For example, in a typical mobile terminated call scenario, an incoming call to the mobile subscriber is first routed to a gateway mobile switching center (GMSC). Upon receiving the mobile terminated call, the GMSC queries the HLR to determine the current location of the mobile subscriber. For example, the HLR typically requests routing information from MSC/VLR and returns it to the GMSC. The GMSC uses the routing information to route the mobile terminated call to the MSC/VLR. The MSC/VLR accesses its subscriber data for the mobile subscriber to determine the location area of the mobile subscriber, and pages the mobile device of the mobile subscriber within that location area to set-up a call connection to the mobile device for the mobile terminated call.
However, if the MSC/VLR crashes, the MSC/VLR goes through a restart routine in which all temporary subscriber records are deleted. During the restart routine (or when the MSC/VLR is in the maintenance stage), subscribers cannot make or receive new calls through the MSC/VLR. To prevent such a loss of service, service providers have begun implementing flexible wireless network architectures. An example of a flexible wireless network 10b is shown in FIG. 2. In the flexible wireless network 10b, multiple MSC/VLRs 30 (i.e., MSC/VLR1 and MSC/VLR2) service a large mobile pool area 80 that is made up of multiple location areas 70 (i.e., LA1-LA5). Each MSC/VLR 30 is able to serve mobile subscribers within any of the location areas 70. A mobile subscriber located in the mobile pool area is registered and served in any one of the MSC/VLRs 30.
However, in the flexible architecture, when one MSC/VLR goes down, another MSC/VLR can take over while the failed MSC/VLR restarts. For example, if a mobile subscriber within LA2 receives a mobile terminated call during the time that the serving MSC/VLR (i.e., MSC/VLR1) is restarting, the mobile terminated call can be routed to MSC/VLR2 for connection of the mobile terminated call to the mobile subscriber. In this case, when the HLR requests the routing information for the mobile terminated call that identifies MSC/VLR1 as the serving MSC/VLR from the HLR 20, a Signal Transfer Point (STP) (within the SS7 network) can forward the request to MSC/VLR2. However, since the LAC of the LA that the mobile subscriber is currently located in is only stored in the serving MSC/VLR, here MSC/VLR1, MSC/VLR2 will not have knowledge of the current location area (LA2) of the mobile subscriber. Therefore, in order to connect the mobile terminated call to the mobile subscriber, MSC/VLR2 must page the mobile subscriber over the entire mobile pool area 80, a procedure commonly referred to as global paging.
Unfortunately, global paging causes excessive traffic throughout the mobile pool area. Therefore, what is needed is a paging solution in flexible wireless network that reduces the traffic within the mobile pool area.